Re: [PATCH 4/4] Documentation: Add device tree bindings for Freescale FTM PWM

[Thierry Reding <thierry.reding@gmail.com>]

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On Wed, Aug 21, 2013 at 11:07:42AM +0800, Xiubo Li wrote:
> Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
> ---
>  .../devicetree/bindings/pwm/fsl-ftm-pwm.txt        | 52 ++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pwm/fsl-ftm-pwm.txt

It used to be that device tree bindings documentation was squashed into
the same commit as the driver. I see some point in splitting this up
given that this will eventually go into a completely separate tree, but
I just want to make sure this is now the official way of splitting
patches so I can tell that to people in good conscience.

> diff --git a/Documentation/devicetree/bindings/pwm/fsl-ftm-pwm.txt b/Documentation/devicetree/bindings/pwm/fsl-ftm-pwm.txt
> new file mode 100644
> index 0000000..698965b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/fsl-ftm-pwm.txt
> @@ -0,0 +1,52 @@
> +Freescale FTM PWM controller
> +
> +Required properties:
> +- compatible: should be "fsl,vf610-ftm-pwm"
> +- reg: physical base address and length of the controller's registers
> +- #pwm-cells: Should be 3. Number of cells being used to specify PWM property.
> +  First cell specifies the per-chip channel index of the PWM to use, the
> +  second cell is the period in nanoseconds and bit 0 in the third cell is
> +  used to encode the polarity of PWM output. Set bit 0 of the third in PWM
> +  specifier to 1 for inverse polarity & set to 0 for normal polarity.
> +- fsl,pwm-clk-ps: the ftm0 pwm clock's prescaler, divide-by 2^n(n = 0 ~ 7).
> +- fsl,pwm-cpwm: Center-Aligned PWM (CPWM) mode.
> +- fsl,pwm-number: the number of PWM devices, and is must equal to the number
> +  of "fsl,pwm-channels".
> +- fsl,pwm-channels: the channels' order which is be used for pwm in ftm0
> +  module, and they must be one or some of 0 ~ 7, because the ftm0 only has
> +  8 channels can be used.
> +- for very channel, the revlatived the pinctrl should be at least two state
> +  {"enN", "dsN"}, which "en" means "enable", "ds" means "disable" and "N"
> +  means the order of the channel.

This is missing a description of the clocks and clock-names properties.

> +
> +Example:
> +
> +pwm0: pwm@40038000 {
> +	      compatible = "fsl,vf610-ftm-pwm";
> +	      reg = <0x40038000 0x1000>;
> +	      #pwm-cells = <3>;
> +	      pinctrl-names = "en0", "ds0", "en3", "ds3";
> +	      pinctrl-0 = <&pinctrl_pwm0_ch0_en>;
> +	      pinctrl-1 = <&pinctrl_pwm0_ch0_ds>;
> +	      pinctrl-2 = <&pinctrl_pwm0_ch3_en>;
> +	      pinctrl-3 = <&pinctrl_pwm0_ch3_ds>;
> +	      fsl,pwm-clk-ps = <7>;
> +	      fsl,pwm-cpwm = <0>;
> +	      fsl,pwm-number = <2>;
> +	      fsl,pwm-channels = <0 3>;
> +	      ...

And this mixes tabs and spaces for indentation.

> +      };
> +
> +leds {
> +	compatible = "pwm-leds";
> +	led {
> +		label = "fsl_led";
> +		pwms = <&pwm0 0 10000000 0>;
> +		max-brightness = <127>;
> +	};
> +	backlight {
> +		label = "fsl_backlight";
> +		pwms = <&pwm0 3 10000000 1>;
> +		max-brightness = <100>;
> +	};

I don't think I like this at all. This example suggests to use the
pwm-leds driver for backlight control. Why not use pwm-backlight
instead?

Thierry

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